Add support for combining accent on webkit (macOS/iOS safari)

[thomassth]

Test URL:
https://fonts.google.com/specimen/Oswald?preview.text=O%CC%82%20%C3%94&preview.text_type=custom
First letter:
U+004F : LATIN CAPITAL LETTER O
U+0302 : COMBINING CIRCUMFLEX ACCENT {hat}
Second letter:
U+00D4 : LATIN CAPITAL LETTER O WITH CIRCUMFLEX

On windows, both letters are rendered correctly:

On Apple systems, the first letter isn't rendered: